Chemical modification of biomolecules is performed to clarify the mechanism for the activity expression of biologically active substances or the function of biomolecules. There is known a method for selectively modifying glycoconjugates with fluorescent dyes, etc., which involves introducing an azido group into biomolecules, e.g., glycoconjugates at the cell membrane surface, etc. and reacting the azido group with triarylphosphines having a fluorescent functional group, etc. as a probe to ligate them through covalent bond (e.g., see Non-Patent Documents 1 to 3).
Also, a method using a single click reaction in which a single azide compound is added and ligated to an alkyne is also known. In this case, probe-bearing biomolecules can be identified by reacting the azido group introduced into the target biomolecule with an alkyne compound as a probe. As examples of the click reaction, a reaction using Cu(I) catalyst and a catalyst-free reaction are both known (e.g., see Non-Patent Documents 4 to 13).